1. Field of the Invention
The present invention relates to a disk recording and/or reproducing apparatus for feeding one of a rotating disk and a pickup relative to the other by a linear motor in the radial direction of the disk, that is, in the tracking direction.
2. Description of the Prior Art
In a compact disk player as an optical disk reproducing apparatus, a tracking control system consists of a fine tracking control system and a coarse tracking control system.
The fine tracking control system controls a tracking mirror or an objective lens so that a beam spot correctly traces the tracks on a compact disk during reproduction in accordance with a tracking error signal. For the system controlling the tracking mirror, a technique disclosed in U.S. Pat. No. 3,944,727 is known. For the system controlling the objective lens, a technique as disclosed in U.K. Pat. No. 1,421,586 or European Patent application publication No. 68757 of the present applicant is known.
The coarse tracking control system feeds an optical pickup by supplying a low-frequency component of a tracking error signal to a feed motor so as to allow the pickup to follow along a feed shaft of a feeding mechanism to compensate for eccentricity of a compact disk itself, eccentricity occurring from chucking, or eccentricity of a disk table.
In this coarse tracking control system, in order to improve response characteristics of servo control, nonlinearity of the feeding operation must be eliminated. For this purpose, the feed shaft of the feeding mechanism is inclined in the radial direction of the compact disk so as to eliminate nonlinearity attributed to friction.
When a track jump is performed in an access mode or the like, that is, when a tracking jump pulse signal is applied to a tracking coil for controlling the tracking mirror or the objective lens and the beam spot is crossing a track, the servo loops of the fine and coarse tracking control systems are open.
Since a linear motor does not have a transmission mechanism for transmitting driving force, the transmission mechanism does not support a movable member.
Therefore, if a linear motor is used as a feed motor of the coarse tracking control system, an optical pickup A tends to slide in the inclined direction of the feed shaft during a track jump by a force W.times.sin .theta. where W is the weight of the optical pickup A and .theta. is the inclined angle thereof, as shown in FIG. 1. If the inclined angle .theta. is sufficiently large, the pickup A actually slides down.
As a result, the track jump in the access mode or the like becomes extremely unstable. Thus, a track jump falling outside the range of a preset number of track jumps is performed, settlement of the optical pickup after the track jump is poor and the access time becomes long.
A method has been proposed by the present applicant in accordance with which a feed signal for feeding in a track jump direction is supplied to the feed motor during a track jump so as to perform the track jump over a distance exceeding a movable distance of the tracking mirror or the objective lens. In this case, if a linear motor is used as the feed motor, and a force generated by the linear motor in response to the feed signal is represented by f, a force f.+-.W.times.sin .theta. is applied on the optical pickup A.
For this reason, in this method, the optical pickup may not be able to jump a predetermined number of tracks or may jump over a predetermined number of tracks.